Two excellent windows, two seasons to avoid
Nepal’s climate follows a straightforward monsoon pattern: two good trekking seasons separated by monsoon (June-September) and winter (December-February). Here is the breakdown.
Autumn (October-November): the peak season
October and November are the most popular months for trekking and for good reason — stable weather, clear skies, excellent mountain visibility after the monsoon has washed the haze away. Daytime temperatures are comfortable, nights cold at altitude. The trails are busy, teahouses full, and permit requirements apply. Book flights and popular accommodation well in advance for October.
Spring (March-May): the second season
March to May is the other excellent trekking window. Less crowded than autumn, rhododendrons blooming on lower trails in March-April, good visibility. May gets warmer at lower altitudes and pre-monsoon clouds start building in the afternoons — still good for trekking, particularly at higher altitudes above the haze.
Monsoon (June-September): avoid for trekking
The monsoon brings heavy rain, leeches on the trails, landslide risk on mountain roads, and poor mountain visibility. Some areas (Mustang, Upper Dolpo) are in a rain shadow and remain trekable during monsoon — the “hidden valleys” season. For most standard treks, avoid.
Winter (December-February): cold but possible
Low-altitude and cultural travel is fine in winter. Kathmandu is cold but not brutal. High-altitude trekking is possible but challenging — passes can be snowed in, temperatures extreme, teahouses may be closed. The Annapurna Circuit’s Thorong La pass is frequently blocked December-February.